Electron discharge device of the magnetron type



P. L. SPENCER Filed Feb. 22, 1945 ELECTRON DISCHARGE DEVICE OF THE MAGNETRON TYPE July 12, 1949.

q, x m s fi M f a W m P fl T 5 X 2 4 2 w g w a Q P 5 m a a a A J 9 m J Patented July 12, 1949 UNITED? STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE OF THE MAGNETRON TYPE Percy L. Spencer, West Newton, Mass., assignor to flaytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application February 22, 1945, Serial No. 579,179

13 Claims. (Cl; 315*) My present invention relates to electron-discharge devices, and more particularly to electrondis charge devices of the magnetron type.

Existing magnetrons comprise, basically, a cathode, an anode appropriately disposed with respect to said cathode, and means for establishing a magnetic held perpendicular to the direction of the electron flow between said cathode and said anode. When used, for example, as an oscillator, such a devicegener'ally requires some sort of external tank circuit, or if itis designed to include a tank circuit, one of its electrodes, usually the anode, is of rather complicated construction. By means of my present invention I seek to avoid these disadvantages;

It is, therefore, an objectof my present invention to provide a magnetron, particularly of the simple, single-anode type, which incorporates a tank circuit in the form of a cavity resonator.

It is another object of my present invention to providesuch a magnetron with means for controlling the resonant frequency thereof.

, It is a further object of my present invention to so construct sucha magnetron as to enable its operation, for example, as an efiicient generator of hyper-frequency oscillations.

In the accompanying specification I shall describe, and in the annexeddrawing show, an illustrative embodiment of the magnetrons of my present invention. It is, however, to be clearly understood that I do not wish to be limited to the details of construction herein shown and described for purposes of illustration only, inasmuch as changes therein may be made without the exercise of invention and within the true spirit and scope of the claims hereto appended.

In said drawing, Fig. 1 is a transverse sectional view of an electron-discharge device made in accordance with the principles of my present invention, and electrically connected, by way of example, as an oscillator; and a Fig. 2 is a transverse sectional view of a modified form of tuning means which may be utilized to control the resonant frequency of such an electron-discharge device. a

Referring now more indetail to the aforesaid illustrative embodiment of my present invention, with particular reference tothe drawing, the nu meral 5 generally design-ates a cathode structure, which may take the form of a hollow cylindrical head 6 closed at its top I, and having its side wall converging, as at 8, to join with a hollow tubular member 9,the outer surfaceof said side wall being provided with an appropriate electron-emist st ng t. a

Disposed within the head 5 is a coiled heater element I I, one end of which is electrically con: nected to said head, for example, to the top 1 thereof, and the other end of which is connected to a lead-in conductor I2 which passes downward- 1y through the tubular member 9, and out of the latter through a glass seal I3. The seal I3 is lodged in a conducting ring I4 which, in turn, is electrically connected to the lower end of the tubular member 9.

Carried by said tubular member 9, adjacent the ring M, is a cup-like member l5, to the upstanding portion of which is secured an insulating ring it which may be made of glass, the upper end of said glass ring being secured to a metallic ring l'l. The upper end of the latter ring reposes in a recess I8 formed in a magnetic pole piece l9, said pole piece having a central bore 20 through which passes the tubular member 9 of the cathode structure 5. The upper face of the pole piece I9 is provided with an annularrecess 2|, in which is disposed a cylindrical apron 22 depending from the head 6 or the cathode structure 5, said apron being spaced from the side walls of the recess 2! and constituting one of the plates of a capacitor which includes said side walls as part of its other plate, and which, as will later be seen, completes the cathode return circuit of the device.

Another cylindrical apron 23, which constl= tutes the remaining part of said other plate of the aforementioned capacitor, is disposed in a recess 24 formed in the upper surface of the pole piece l9, this apron, in turn, supporting a toroidal member 25, providedwith an annular opening 26 in the inner wall thereof and constituting a cavity resonator.

The dimensions of the toroid are preferably such that the resonant frequency thereof is in the micro-wave region.

Carried by the toroidal member 25, surrounded thereby and connected thereto on the side of the opening 26 opposite tothat which is connected to the apron 23, is a cylindrical plate 21 constituting an anode, the latter being separated from the coated cathode head 6 by the electron-discharge space 28 which communicates with the interior of the cavity resonator 25 through the opening 26.

The upper end ofxthe anode 21 is disposed in a recess 29 formed in a second magnetic pole piece 30, the latter, together with the pole piece 19, being adapted to establish a magnetic field there between Whose axis is perpendicular to the di rection of the electron flowbetween the cathode head Band the anode I.

When the device is used, for example, as an oscillator, the anode 2! may be connected, throughea conductor 3|, to the positive terminal of a source 32 of E. M. F., and the cathode structure 5 may be connected, through a conductor 33, to the negative terminal of said source of E. M. F. The heater element ll may be connected to another source 34 of E. M. F. through a portion of the conductor 33 and another conductor 35. By properly proportioning the magnitude of the potential difference between the cathode 5 and anode 27, and the intensit of the magnetic field between the pole pieces I9 and 30, the electrons emitted by the cathode coating T may be made to so oscillate, or move about in such orbital paths within the discharge space 28 between said cathode and said anode, as to excite the cavity resonator 25 into hyper-frequencyoscillations.

In order to extract power from the device, the resonator may be provided with a pipe 36 extending therefrom and communicating with the interior thereof, said pipe having, at its outer end, a glass seal 31, and a pick-uploop 38, adapted to a couple with the magnetic component of the oscillations within said resonator, entering said resonator through said glass seal and said pipe. The outer ends of the pick-up loop and the pipe may .join with any preferred transmission line, for example, a coaxial line, to convey the extracted power to any utilization device or circuit.

While the device as thus far described will, of course, have a natural resonant frequency depending, in a well known manner, upon the dimensions and spacing of the various components thereof, I prefer to incorporate therein controllable means for altering said resonant frequency, and while not limited thereto, I may utilize, for this purpose, electronic tuninggsuch as may be obtained by the apparatus disclosed in the copending application of Palmer P. Derby, entitled Electron discharge device, Serial No: 569,873, filed December26, 1944.

As disclosed in said copending application, and as shown in the drawing herein, this device includes a pipe 38 extending outwardly from the cavity resonator 25, said pipe being provided, at the outer end thereof, with a glass seal 39 having a reentrant stem 40. Three lead-in conductors 4|, 42, and 43 pass through said stem 40, the conductor ll being connected with a cylindrical shield 44 coaxially supporting therein an electron-emissive cathode 45, the conductor 42 being connected to one end of a heater element 46 disposed within the cathode 45 and having its other end connected thereto, and the conductor 43 being connected to a cylindrical cap 4'! provided with an aperture 48 in its front wall, which aperture is covered with a fine-mesh accelerator grid 49.

The lead-in conductors 4| and 42 are connected, through conductors 50 and to a source 50' of E. M. F., whereby current is conveyed to the heater element 45 to raise the temperature of the cathode 45 to the necessary level for electron emission. The lead-in conductor 43 is connected, through a conductor 52 and a variable tap 53', to an appropriate point on the source 50 of E. M. F., whereby the grid 49 is made positive with respect to the cathode 45, and the electrons emitted by the latter are accelerated and directed into the inner space of the cavity resonator 25. These electrons are eventually captured by the wall of the resonator. The efiect of shooting electrons into the resonator is to change the dielectric constant of the space therein, and therefore the capacitance thereof, whereby the resonance of said resonator becomes altered in a well known manner. The deviation from the natural resonant frequency of the resonator depends upon the concentration of electrons entering the same, and this is controlled by the magnitude of the positive bias on the grid 49. Thus, by altering said positive bias, the output of the magnetron may, if desired, be frequency modulated.

Means other than electronic tuning may be utilized to control the frequency of the magnetron of my present invention. Such another means is shown in Fig. 2 of the drawing. This is known as plug tuning. and may take the following form.

The outer wall of the cavity resonator 25 may be provided with an opening 54- in which there may be mounted, in a manner to permit sliding the same into the space withinsaid resonator, a cylindrical plug 55. Any suitable means may be utilized to effect said sliding movement, but I prefer to provide the plug, at its outer end, with a recess 56 receptive of a washer 51, said washer being retained within said recess by a cap 58 threadedly engaged with the plug. The washer is rotatably mounted on'the inner end'of a rod 59 threadedly engaged in a cap 60 and provided with a manipulating head-Bl at its outer end. The cap 60 closes the outer end of a tubular member 62 mounted on and extending" outwardly from the cavity resonator 25. In order to help maintain the .plug in any given adjusted position, I provide a bellows-like member 63 anchored, at one end, to the plug and, at the other end, to the cap and tubular member 62. Movement of the plug into or out of the resonator alters the inductance of said resonator and thereby enables tuning the same to a frequency other than the natural resonant frequency thereof.

This completes the description of the aforesaid illustrative embodiment of the magnetrons of my present invention. It will be noted from all'of the foregoing that I have provided a simple, singleanode type of magnetron with a tuned circuit in the form of a cavity resonator, whereby the same may constitute a self-contained oscillator which may be utilized to generate hyper-frequency oscillations. It is, however, to be understood that the. device is not limited to this use. 7'

It will further be noted that the magnetrons of my present invention are so constructed as to enable their ready tuning to frequencies other than the natural resonant frequency thereof; but here again, I do not wish to be limited to the two types of tuning specifically shown and described herein.

Other objects and advantages of the devices of my present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. An electron discharge device comprising: a first electrode having an electron-emissive surface; a second electrode spaced from and symmetrically disposed about said first electrode; means for establishing a magnetic field intermediate said electrodes perpendicular to the direction of the electron flow therebetween; a coupling device having a terminal electrically connected to said first electrode; a cavity resonator surrounding said second electrode, and connected between the same and a second terminal on said coupling device; and means, carried by said cavity resonator, for tuning said cavity resonator.

2. An electron discharge device comprising: a. first electrode having an electron-emissive surface; a second electrode spaced from and sym-r 5 metrically disposed about said first electrode; a role piecesecumd to acnof'said electrodes; said inlet-niece bein adant d to establish a ma n tic ield intermediate said electrodes perpendicular odhedirectionnfthe e1 ectron nowthereb tween; t coupling a terminal electrically connected to aid f rst electrode; a toroidal vcavity resonator urrounding said secondelectrode, and connected tetween the same and a second terminal on said :onpling device; and means, carried :by said oavty resonator, 'for tuning said cavity resonator.

,3. electron discharge device comprising: a inst elect-rode having anelectron-emissive sura e; zagsecond electrode spaced from and symnet zi ally disposed about said first electrode; neans ,fOI' establishing .a magnetic field intermel iate lsaid electrodes perpendicular to the direcion of theqelectron flow therebetween; a capaci- 1M9 impedance having a terminal electrically :gnnfictedtto said first electrode; a cavity resonaorzsurnounding said second electrode, and coniected between thesame and a second terminal mtsaid capacitive impedance; and means, car- 'idd rbyisaid cavity resonator, "for tuning said cavtynesonator.

14. electron discharge device comprising: a irst lelectrode having an electron-emissive suriace; a second electrode :spaced fromand sym, netrically disposed about said first electrode; means for establishing a magnetic field inter,- nediate said electrodes perpendicular to the diectionlof the electron .fiow therebetween; a couiling device having a terminal electrically coniected to said first electrode; a toroidal cavity resonatorsurrounding said second electrode, and iaving an annular opening communicating with he discharge space intermediate said electrodes; he wall of said cavity resonator being connected, )n oneside of said annular opening, to saidsec- )ndelectrode and, on the otherside of said aniular opening, to a second terminal on said cou- Jling ,device; and means, carried by said cavity :esonator, for tuning said cavity-resonator.

,5. An electron discharge device comprising: ;a

first electrode having an ,eleotron-emissive surlace; (:3 second electrode-spaced "from and symnetrically disposed about said first electrode; a 3018 piece securedto eachof said electrodes; said aole pieces being adaptedztolestablish a magnetic ield intermediate saidaelectrodes perpendicular to t;

;he direction of the electron flow therebetween; i first cylindrical apron carried by said first electrode; a second cylindrical apron spaced from and concentric with said first cylindrical apron; aaid cylindrical aprons constituting a capacitive vmpedance; a toroidal cavity resonator surround- .ng said second electrode, and having an annu- .ar opening communicating with the discharge ipace intermediate said electrodes; the wall of ;aid cavity resonator being connected, on one ;ide of said annular opening, to said second elecnode and, on the other side of said annular open- ,ng, to said second cylindrical apron; and means, :arried by said cavity resonator, for tuning said :avity resonator.

6. A hyper-frequency oscillator comprising: a :athode having an electron-emissive surface; an anode spaced from and symmetrically disposed about said cathode; means, coupled to said cath- Jde and anode, for establishing a, potential difference between asid cathode and said anode; means for establishing a magnetic field intermediate said cathode and said anode perpendicular to the direction of the electron flow therebetween; the relative magnitudes of said potential differfaced cfi ti etnd s mm t dismsed a out dlcathc i coupled said Bath? ode anodaw c establish n a p nt tieten c tc we n ai cathod a d aid a o e; me ns tie es abl s in a .maen t :fi ld in ermediate sai patheti and saida ode p pendicula to the dir cti no el ctron :fiow therebetween; the relative magnitudes of said potential differ- $21 .06 landtsaid ma neti Jfie db in such that t electr mitted by said cathode are caused to 9 'llatcti-n the spac between said cath de and anpd ste oida av y-resonatorconnected ith and surrounding said anode; said resonator haying an annnlar opening in 1 its wall communitcatin tvith the d schar spac int rm diate said eat odeand .saidanOda wher y it s a t to becom {excite bys rid el ctron s i l tions; nd a ,wqirnpedance ,coupling intermediate said ,cavity w-rcsonator and said cathod to compl te the A-=lC.,ci iQl b twfifimsn di athod and saidan de.

n lhype efrequsn y os illa r co p is a Cathode l tt in n slB tron-emissive surface; an anode spaced from and symmetrically disposed aboli lsaid. cathode; means, coupled to said catnode and anode, for establishing aqpotential dittference between said cathode and said anode; meansyfcrestablishin taxmagnetic :field intermediate said cathode and saidlanode perpendicular to -tthe direction .of i the electron flow ,therebetween; cthe relative ,magnitudes of said potential diiference and :said r; magnet1c field being such thatlllhe electrons emitted by said cathode are caused to ,oscillate win the space between said cathode and said anode a cavity resonator con,- nected ,with and surrounding said anode, and adapted :to be excited by said .electron (oscillations; means carried byisaid resonator for controllin the frequency ofnexcitation thereof; and a rlowsimpedance .-coupling:intermediate said cavity resonator :and said :C'cathode to complete the A.-C. circuit between said cathode and said anode.

9. A hyper-frequency oscillator comprising: a cathode having an electron-emissive surface; an anode spaced from and symmetrically disposed about said cathode; means, coupled to said cathode and anode, for establishing a potential difference between said cathode and said anode; means for establishing a magnetic field intermediate said cathode and said anode perpendicular to the direction of the electron flow therebetween; the relative magnitudes of said potential difference and said magnetic field .being such that the electrons emitted by said cathode are caused to oscillate in the space between said cathode and said anode; a toroidal cavity resonator connected with and surrounding said anode; said resonator having an annular opening in its wall communicating with the discharge space intermediate said cathode and said anode, whereby it is adapted to become excited by said electron oscillations; means carried by said resonator for controlling the frequency of excita- 75 tion thereof; and a low-impedance coupling in-.

termediate saidcavity resonator and said cathode to complete the A.-C. circuit between said cathode and said anode. I

10. An electron-discharge device comprising: a pair of spaced electrodes adapted to support an [electron flow therebetween; a pair of pole pieces secured, respectively, to said electrodes and [adapted to establish a magnetic field therebetween in a direction perpendicular to said electron flow; one of said pole pieces being provided with a recess the walls of which constitute a terminal of a coupling device between said electrodes; a conductive member electrically connected to one of said electrodes and extendin into said recess; said conductive member constituting another terminal of said coupling device; and a cavity resonator electrically connected between said recessed pole piece and the other of said electrodes. 7

11. An electron-discharge device comprising: a pair of spaced electrodes adapted to support an electron fiow'therebetween; a pair of pole pieces secured, respectively, to said electrodes and adapted to establish a magnetic field therebetween in a direction perpendicular to said electron fiow; one of said pole pieces being provided with a recess the walls of which constitute one plate of a capacitive impedance between said electrodes; a conductive member electrically connected to one of said electrodes and extending into said recess in spaced relationship to the walls thereof; said conductive member constituting another plate of said capacitive impedance; and a cavity resonator electrically connected between said recessed pole piece and the other of said electrodes.

12. An electron-discharge device comprising: a first electrode having an electron-emissive surface; a second electrode spaced from and symmetrically disposed about said first electrode; said electrodes being adapted to support an electron fiow therebetween; a pair of pole pieces secured, respectively, to said electrodes and adapted to establish a magnetic field therebet-ween in a direction perpendicular to said electron flow; one of said pole Pieces being provided with an annular recess the walls of which constitute one plate of a capacitive impedance between said electrodes; a cylindrical, conductive apron electrically connected to said first electrode and extending into said recess in spaced relationship to the walls thereof; said conductive apron consti tuting another plate of said capacitive imped ance; and a toroidal cavity resonator surround ing said second electrode and electrically con nected between said recessed pole piece and sail second electrode.

13. An electron-discharge device comprising a first electrode having an electron-emissive sur face; a second electrode spaced from and sym metrically dis-posed about said first electrode said electrodes being adapted to support an elec tron fiow therebet-ween; a pair of pole pieces se cured, respectively, to said electrodes and adapt ed to establish a magnetic field therebetween ii a direction perpendicular to said electron flow one of said pole pieces being provided with a! annular recess the walls of which constitute om plate of a capacitive impedance between salt "electrodes; a cylindrical, conductive apron electrically connected to said first electrode and extending into said recess in spaced relationship ti the walls thereof; said conductive apron constituting another plate of said capacitive impedance; and a toroidal cavity resonator surrounding said second electrode and having an annulai opening communicating with the space betweer said electrodes; the wall of said cavity resonatoi bein electrically connected, on one side of saic annular opening, to said recessed pole piece and on the other side of said annular opening, to saic second electrode.

- PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,125,280 Bieling Aug. 2, 1938 2,167,201 Dallenbach July 25, 1935 2,270,638 Llewellyn Jan. 20, 1945 2,272,211 Kohler Feb. 10, 1942 2,314,794 Linder Mar. 23, 1945 2,351,744 Chevigny June 20, 1944 2,407,974 Cliiford et al. Sept. 24, 1946 FOREIGN PATENTS Number Country Date 509,102 Great Britain July 11, 1939 Certificate of Correction Patent No. 2,475,646. July 12, 1949.

PERCY L. SPENCER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 6, claim 2, after the Word coupling insert device having;

end that the said Letters Patent should be read with this correction therein that the same may conform to the record of the ease in the Patent Oflice. Signed and sealed this 29th day of November, A. D. 1949.

THOMAS F. MURPHY,

Assistant Gommz'ssz'oner of Patents. 

